Mining the Moon

Mining the Moon

Helium-3 advocates claim that it, conversely, would be nonradioactive, obviating all those problems. But a serious critic has charged that in reality, He3-based fusion isn’t even a feasible option. In the August issue of Physics World, theoretical physicist Frank Close, at Oxford in the UK, has published an article called “Fears Over Factoids” in which, among other things, he summarizes some claims of the “helium aficionados,” then dismisses those claims as essentially fantasy.

Close points out that in a tokamak–a machine that generates a doughnut-shaped magnetic field to confine the superheated plasmas necessary for fusion–deuterium reacts up to 100 times more slowly with helium-3 than it does with tritium. In a plasma contained in a tokamak, Close stresses, all the nuclei in the fuel get mixed together, so what’s most probable is that two deuterium nuclei will rapidly fuse and produce a tritium nucleus and proton. That tritium, in turn, will likely fuse with deuterium and finally yield one helium-4 atom and a neutron. In short, Close says, if helium-3 is mined from the moon and brought to Earth, in a standard tokamak the final result will still be deuterium-tritium fusion.

Second, Close rejects the claim that two helium-3 nuclei could realistically be made to fuse with each other to produce deuterium, an alpha particle and energy. That reaction occurs even more slowly than deuterium-tritium fusion, and the fuel would have to be heated to impractically high temperatures–six times the heat of the sun’s interior, by some calculations–that would be beyond the reach of any tokamak. Hence, Close concludes, “the lunar-helium-3 story is, to my mind, moonshine.”

Close’s objection, however, assumes that deuterium-helium-3 fusion and pure helium-3 fusion would take place in tokamak-based reactors. There might be alternatives: for example, Gerald Kulcinski, a professor of nuclear engineering at the University of Wisconsin-Madison, has maintained the only helium-3 fusion reactor in the world on an annual budget that’s barely into six figures.

Kulcinski’s He3-based fusion reactor, located in the Fusion Technology Institute at the University of Wisconsin, is very small. When running, it contains a spherical plasma roughly 10 centimeters in diameter that can produce sustained fusion with 200 million reactions per second. To produce a milliwatt of power, unfortunately, the reactor consumes a kilowatt. Close’s response is, therefore, valid enough: “When practical fusion occurs with a demonstrated net power output, I–and the world’s fusion community–can take note.”

Still, that critique applies equally to ITER and the tokamak-based reactor effort, which also haven’t yet achieved breakeven (the point at which a fusion reactor produces as much energy as it consumes). What’s significant about the reactor in Wisconsin is that, as Kulcinski says, “We are doing both deuterium-He3 and He3-He3 reactions. We run deuterium-He3 fusion reactions daily, so we are very familiar with that reaction. We are also doing He3-He3 because if we can control that, it will have immense potential.”